G-SYNC 101: In-game vs. External FPS Limiters

Closer to the Source

Up until this point, an in-game framerate limiter has been used exclusively to test FPS-limited scenarios. However, in-game framerate limiters aren’t available in every game, and while they aren’t required for games where the framerate can’t meet or exceed the maximum refresh rate, if the system can sustain the framerate above the refresh rate, and a said option isn’t present, an external framerate limiter must be used to prevent V-SYNC-level input lag instead.

In-game framerate limiters, being at the game’s engine-level, are almost always free of additional latency, as they can regulate frames at the source. External framerate limiters, on the other hand, must intercept frames further down the rendering chain, which can result in delayed frame delivery and additional input latency; how much depends on the limiter and its implementation.

RTSS is a CPU-level FPS limiter, which is the closest an external method can get to the engine-level of an in-game limiter. In my initial input lag tests on my original thread, RTSS appeared to introduce no additional delay when used with G-SYNC. However, it was later discovered disabling CS:GO’s “Multicore Rendering” setting, which runs the game on a single CPU-core, caused the discrepancy, and once enabled, RTSS introduced the expected 1 frame of delay.

Seeing as the CS:GO still uses DX9, and is a native single-core performer, I opted to test the more modern “Overwatch” this time around, which uses DX11, and features native multi-threaded/multi-core support. Will RTSS behave the same way in a native multi-core game?

Yes, RTSS still introduces up to 1 frame of delay, regardless of the syncing method, or lack thereof, used. To prove that a -2 FPS limit was enough to avoid the G-SYNC ceiling, a -10 FPS limit was tested with no improvement. The V-SYNC scenario also shows RTSS delay stacks with other types of delay, retaining the FPS-limited V-SYNC’s 1/2 to 1 frame of accumulative delay.

Next up is Nvidia’s FPS limiter, which can be accessed via the third-party “Nvidia Inspector.” Unlike RTSS, it is a driver-level limiter, one further step removed from engine-level. My original tests showed the Nvidia limiter introduced 2 frames of delay across V-SYNC OFF, V-SYNC, and G-SYNC scenarios.

Yet again, the results for V-SYNC and V-SYNC OFF (“Use the 3D application setting” + in-game V-SYNC disabled) show standard, out-of-the-box usage of both Nvidia’s v1 and v2 FPS limiter introduce the expected 2 frames of delay. The limiter’s impact on G-SYNC appears to be particularly unforgiving, with a 2 to 3 1/2 frame delay due to an increase in maximums at -2 FPS compared to -10 FPS, meaning -2 FPS with this limiter may not be enough to keep it below the G-SYNC ceiling at all times, and it might be worsened by the Nvidia limiter’s own frame pacing behavior’s effect on G-SYNC functionality.

Needless to say, even if an in-game framerate limiter isn’t available, RTSS only introduces up to 1 frame of delay, which is still preferable to the 2+ frame delay added by Nvidia’s limiter with G-SYNC enabled, and a far superior alternative to the 2-6 frame delay added by uncapped G-SYNC.

Should “Reduce Buffering” option in Overwatch be enabled or disabled? Many competitive/pro players suggest having reduce buffering on to get higher framerate and reduced input lag but would having this option on have a negative effect on G-SYNC?

Also I recently upgraded my system to a i7-8700k and 1080ti. I usually sit at a steady 300fps on Overwatch now and use a 240hz monitor (Asus PG258Q). Would G-SYNC be worth using in this case?

“Reduced Buffering” is effectively Overwatch’s version of Nvidia’s “Maximum pre-rendered frames” set to “1,” so yes, leave it enabled for the lowest input lag, and no, it does not interfere with G-SYNC functionality; it was enabled for all the tests in this article. As for 240Hz G-SYNC w/238 or 237 FPS limit vs. 240Hz V-SYNC OFF w/238 or 237 FPS limit, the lag difference is almost zero; see the 240Hz chart on this page here. And for 240Hz G-SYNC w/238 or 237 FPS limit vs. 240Hz V-SYNC OFF at 300 FPS, you’re only looking at a 1ms difference in lag,… Read more »

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5 months 18 days ago

Member

pervyjutsu

So I’ve been experimenting with the different kinds of settings: – 240Hz G-SYNC w/ 238 or 237 FPS limit – 240Hz V-SYNC OFF w/ 238 or 237 FPS LIMIT – 240Hz V-SYNC OFF w/ 300 FPS limit I actually found myself liking 240Hz V-SYNC OFF w/ 238 or 237 FPS LIMIT the best. Up until now I have always used 300 FPS limit because that is what everyone said was best input lag-wise, but after trying the lower 238 or 237 limit today, wow I can aim so much better for some reason? It is definitely not placebo because I… Read more »

We always have to consider the (never to be underestimated) placebo effect, but… Like I mentioned in my last reply, the unique way each of those various scenarios deliver frames could be causing subtle differences in lag patterns that may affect aiming; muscle memory, conditioning, subconscious processes, etc. Because quite frankly, unless Overwatch is doing something abnormal with a 300 FPS limit above your refresh rate (which none of my existing tests show), or you’re experiencing a system specific issue, then the scenario you’re claiming feels more responsive, is actually slightly less responsive, at least where raw average input lag… Read more »

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5 months 17 days ago

Member

bcbuse

First, this is the best Gsync/Vsync information on the internet. I appreciate the effort you put into this, well done.

I read a comment you posted somewhere that ‘technically’ the absolute least input lag would be with Gsync Off + Vsync Off + Framerate upcapped(getting at least 2x the monitor refresh rate). Can you approximate how much less input lag that would be versus Gsync On + Vsync On(NVCP) + Framerate capped 2 below monitor refresh rate?

Depends on the maximum refresh rate and how high the framerate is sustained above it, but at 2x ratio, and at higher refresh rates, you’re looking at only 1-3ms less average input lag with G-SYNC off + V-SYNC off + FPS uncapped vs. G-SYNC on + V-SYNC on + -2 FPS limit when measured at crosshair level.

You can see the worst case first reaction differences between those two scenarios on the ninth page here.

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5 months 19 days ago

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daniel8747

to clarify: with fps capped 2-3 fps below monitor refresh rate, do i still need to have v-sync enabled?

Sort the comments here by newest; the answer is in the reply to the comment below yours, as well as in the “Range” section of this article.

Short answer to your question is “yes,” but only if you never want to see tearing.

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15 hours 35 minutes ago

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SturmButcher

I don’t understand something…. Why do I need V-Sync on with G-Sync?, The last one already sync frames and If I use a frame limiter I would never need V-Sync, I don’t understand guys. I am suspecting that G-Sync+V-Sync+RTSS is causing stutter in some games…Could you please enlighten me?

I’ve explained this ad nauseam (including in this article), but I’ll try to break it down as clearly as possible yet again… Within the G-SYNC range (e.g. within the refresh rate), G-SYNC is V-SYNC, and V-SYNC is G-SYNC. The “V-SYNC” option in the “on” position with G-SYNC enabled was originally a non-optional part of G-SYNC. It was only at a later point Nvidia revealed the V-SYNC “on/off” option in the control panel so that the screen would tear with V-SYNC “off” when the framerate exceeded the G-SYNC range/refresh rate, instead of reverting to V-SYNC behavior. However, the V-SYNC option also… Read more »

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16 days 4 hours ago

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vityapapa

The Csgo input-lagg is the best g-sync off+v-sync off and fps_max 0? i have 144hz monitor.